In recent years, a range image system utilizing an optical-path-difference detection method is known (see U.S. Pat. No. 6,057,909, for instance). In this detection method, infrared pulsed light is emitted to a space to be shot, and the pulsed light reflected by a subject is taken after a predetermined period to obtain a subject image (range image) residing at a position of a predetermined distance (optical path difference). The range image system described in the above-noted US Patent employs a solid-state imaging device for receiving the infrared light. Further, a high-speed shutter device of an electrooptical shutter, an image intensifier and so forth is provided for the purpose of receiving only the pulsed light reflected by the subject located at the predetermined distance.
With respect to the range image system, obtaining a normal visible-light image simultaneously with the range image is useful in clipping a specified subject from the image (in separating the background) and in producing a three-dimensional image. However, the solid-state imaging device employed in the range image system is intended to receive the infrared light. Thus, another solid-state imaging device for receiving the visible light is required to simultaneously obtain both of the range image and the visible-light image. In addition, a prism and so forth are also required for guiding incident light to the respective solid-state imaging devices.
In this regard, the assignee of this application proposes a solid-state imaging device in which a structure of the range image system is simplified for the purpose of improving its size and its cost (see Japanese Patent Application No. 2006-172649). This solid-state imaging device is capable of simultaneously receiving the visible light and the infrared light, although a single plate structure is adopted. This solid-state imaging device is also capable of independently controlling light receiving periods of the infrared light and the visible light. By employing this imaging device, the prism and the shutter device become unnecessary so that the structure of the range image system is simplified.
By the way, the above-mentioned range image system obtains the range image by using the infrared light having a wavelength which is different from that of the visible light, so as not to affect a human gaze and normal shooting. However, the infrared light actually entering the range image system includes not only reflection component of the pulsed light, which is emitted from an infrared emitting device and is reflected by a subject, but also infrared-light component existing in the ambient light of the sunlight, the incandescent light and so forth. Due to this, range imaging is affected. Consequently, there arises a problem in that an S/N ratio of the range image remarkably deteriorates in some conditions and it is impossible to correctly obtain range information.